I don't own any of these models, nor have I seen any in person; these are some of the things I've noticed looking at pictures. Please correct me on any of my observations/information.
1/18 TSM (General): All of the TSM F1 models (GTR, LM) share a few shortcomings. The OZ wheels are inaccurate in shape with spokes that are too thin and offsets that are a bit deep. The all around stance is wonky; the front track is too narrow (especially noticeable on the LM and '96 GTRs due to the fender flares) and the rear looks jacked up (the tire sizes - short front, tall rear - might be at fault). That said, I think TSM captured the body shape quite well. For example, comparing the TSM and AutoArt LM models, the shape of the headlight areas appear more correct on the TSM while the AutoArt "brows" look droopy.
1/18 TSM Ueno Clinic: The glaringly obvious mistake here is the absence of 01R's front fender flares. The colors appear a few shades too bright, although that might just be the photos.
1/18 TSM Harrods: This one doesn't have any stand out inaccuracies at first glance. In regards to the taillights, this model shows the car in one of its '95 configurations. GTR 06R is one of the '95 cars that was later updated to '96 specifications. Easy-to-spot body changes include the addition of integrated front flares, the extension on the roof air-inlet and (as you noticed) the smaller taillights set deeper into the bodywork. So in a way you were correct in questioning the models accuracy. It just depends on when your reference picture was taken.
The model has the incorrect '96 front bonnet for a model of 06R in its '95 guise.
1/18 TSM Gulf: Going off of GTR 02R (when it ran #24) the model is missing the same flares as the 01R model (which is strange, because TSM's 1/43 of 02R
has the flares). As a '95 this car also has incorrect taillights (the actual car still retains its '95 spec bodywork).
1/18 TSM Fina: This one seems all around correct with the right aero work. Subtle differences in the actual car can be seen across photographs. The air inlet and side skirts for example. This model has the extended roof-air inlet (which looks a bit shallow on the model compared to the real thing) and the full length skirts; I've seen photos of 16R with and without these features. I believe 18R also has the #38 Fina livery (currently).
1/18 TSM Lark: This one also appears to be fine all around. The models likeness seems true to 14R (during its career) and/or 04R (as it appears today).
It might be worth mentioning that the things I have mentioned above are based off of the pictures on TSM's website. I'm not sure if the models are shown are pre-production or the issued product.
-
Straying from the topic a little bit, I think the nicest offering in 1/18 scale is from HPI (again, this is based one pictures). I'm not sure what availability is like as I believe HPI is no longer in business. For comparison's sake, here are the TSM and HPI 01R models:
TSM
HPI
A lot of detail photos of the HPI model can be seen in this thread on
Diecastxchange. In addition to the Ueno Clinic livery, the
HPI website shows the short tail in two Lark liveries (#60, #61) and the long tail in Fina, Loctite and Lark (#44 Suzuka, #44 Le Mans). One big catch with these models is that they are a curbside (no opening features). Fortunately, for myself, I am into the smaller scales so I don't have to face this sort of dilemma.
One more thing for thought. If you are a tinkerer, a TSM model might make a really good starting point for a
great model. More accurate wheels and tires (I'd try reaching out to AutoArt to see if you can purchase "repair" parts) and some adjustments to the suspension would make a TSM first rate.