It doesn't appear on the Scalecoat listing.
I still have a bottle of it in my stash.
#54 QUICK DRY
Direction:
For use on plastic, this additive will dry SCALECOAT from fast to immediate depending on the amount mixed in the paint. Mix up to equal parts to paint for immediate drying. If mixed with the paint, thinner myst be added if it is to be sprayed.
Looks to me that this additive was made to make Scalecoat I plastic-compatible. Since the Scalecoat II was introduced, there is no longer a need for this additive.