It's not made absolutely clear in the text of the technique (it is an aide memoire rather than an instruction manual after all) but, according to the ISTD, there are three forms of the spot turn, one of which employs a switch action.

Strictly speaking this form of the spot turn should be referred to as a spot turn with a switch action. Colloquially, however, it's referred to as a switch turn. The switch turn is characterized by the prescribed and invariant amount of turn between step 1 and step 2: half a turn.

In the other two forms of the spot turn the amount of turn between step 1 and 2 is not prescribed. The difference between these forms is as follows. In one form in order to take step 2 the foot is moved so that the turn is taken around a notional object. This is similar to the turn which forms part of the alemana. In the other form as step 2 is taken one point within the ball of the stepping foot remains in place; the turn is therefore "tighter".

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I guess it should not be the same kind of turn, but in the ISTD Latin American Rumba manual, page 30 starts with the title:
SPOT TURNS (including Switch Turns and Underarm Turns)
Then it says: "Spot Turns are three forward steps danced...circling...If preferred when turning L the ball of LF may remain in place while turn is made around this foot."
Next page: Switch turn to left: Foot position: RF fwd in line with LF, then turn to end RF back.
Is the same technique applicable to both turns?
On the other hand, Walter Laird's Technique of latin dancing explains tnat the foot position of the first step of the spot turn is "RF/LF fwd and acroos body turning to finish RF/LF back and slightly to side".
So, how do you dance the Spot turn?

In a spot turn, the first step is a forward walk, turning. So if you have been facing partner, you step across the body, making a foot swivel on the standing foot, so that your step lands "forward" (ie just the same as a New York).

You swivel 1/2 turn on the standing foot, and replace weight back to the other foot.

The last step is also a forward walk turning, and it swivels, once the weight is over it, back to face partner.

One area of difference between Switch & Spot Turns, is direction, as a Switch Turn will usually commence towards partner, rather than across the body, to the side. Other than that, I can't think of a difference between them.

If what I see is correct the Spot Turn is being called a Switch Turn. The foot stays in place on the turn. On the other we now have have a movement of the foot towards the standing foot and out again. To some it might feel like a Ronda movement of the once stationary foot.
If any look at the Rumba Int,Style. Spot Turn and Underarm Turn on this site you will notice the movement of the one upon a time stationary foot.
To make things even more confusing. If we call an Under Arm turn a Switch Turn ( which is the old Spot Turn ) we wont be far wrong.
Even what was once an Alemana is substituted for a Switch Turn by some.
Go in on the mans left side and turn a half a Turn and come out without any brushing of the right foot to the left. If taking an examination stick to the book. If a Spot Turn to the left keep that left foot in place.
Does anybody else think that the description in the books of an Alamana leaves a lot to be desired.Is it about time that the books are brought up to date to coincide with the way the different moves are being taught and performed today by our best teachers and dancers..

Something worth pointing out is from a comment made by G Hearn on a Letter Service Tape. Why on a Spot Turn or any simular turn do we step across our body. Answer is. If we step straight and turn we will finish with our feet crossed up.We should be able to start as a Spot Turn and change our mind and go into a Backward Walk which if the feet are crossed up is not going to be as clean and precise as it should be. The same thing happens all the time when the lady does a Cross Body lead to the Fan Position. This is the movement Hearn was discusing.

There are no CBL in Intern. style latin, thats an American style " version ". It actually was developed from WC Swing .

Terence. Originally and for many years in the ISTD Revised Edition in their Rumba there was no New York. There is now I beieve.
The part which I call a Cross Body Lead is steps 4 5 6 of a Closed Hip Twist. Those 3 steps are used often from other positions. Call it what you will, it still gets the lady out to the man's left side moving across the front of his body. Let us all raise our hats to West Coast Swing.

Again, terminology has quite different meanings in some cases. The NY to which you refer, is a Crossover break in Amer. style.

A CBL is a completely diferent lead and body position ,than that preceding a Fan. It is not only a different variation in content; but is also used in many of the Smooth dances ,as well as Rhythm.

What should be known is this..the " english " re- named several Standardised American variations, in an attempt to create a new paradigm.
Also to consider, the technique for comparable figures is completely different in most cases .

Terence. If you were asked to give a name to steps 4 5 6 of the Closed Hip Twist for the lady which is. Step LF on beat 2. Step and turn at the end of beat 3 with the RF. Step back ( a Backward Walk ) on the LF on beats 4 1. The lady is now in the Fan Position.
Those three steps can be used from dozens of positions and shapes.
What name would you give it if it wasn't part of the Closed Hip Twist. The easy way out I suppose would be to call 4 5 6 of the Closed Hip Twist.
If we go to another dance , the Waltz. We have 4 5 6 of a Reverse Weave which becomes, if we do a Chasse to the Right an Outside Change. Identical steps in both cases. The day will come when somebody will have to unraval the name of the steps in most of our dances to get them into a book form that can be understood. I'm still reading Wally Laird and Alex Moore. The others I haven't bothered to get.

You can "take " components from many figures and see similarity in content. That , in and of itself, does not qualify it as being the same.

The differences are there for a reason .The styles of the 2 divisions ( Amer.. Intern. ) are bound to have some similarities as they are from the same roots . However.. they are danced comletely different at Social and competitive levels in all dances .

What has happened over the yrs is this.. the Amer. Smooth has taken on many of the Intern. style figures as part of its syllabi at advanced levels ( some have been there since the 50s, in "Gold" ).VW has an abundance of variations that are used in comp. work.

The comparisons in the Rhythm dances is generally more distinctive, tho some would say that has also made a move towards the Intern. in style particularly in Cha and Samba .