Compatabilities:
CT Bk2: Designs not compatible with most other systems. Most components compatible.
CTHG and T20: both use the exact same rating system for their combat statistics, and T20 expands a few options. about 98% compatible
MT: ratings used are the same as CTHG (and thus T20), but the fundamentals of designs do differ. I've used CT designs from Supp9 in MT games as agressors. Absolutely no issues there. Biggest differences: Controls vs bridge, fuel requirements (PP & JD)
TNE & T4: designs compatible to each other, ratings not. Rerate from designs. Designs not entirely compatible with anything else. Many components not comparable with other editions (Bridge, MD, Weapons, LS); nature of MD different from other editions.
GT: designs not compatible with any other designs. Ratings not compatible. Most components comparable to CTHG/MT/T20
MGT: Design system fairly compatible with CTBk2, most components compatible with CTHG/MT/T20. Most plans compatible with CTBk2 plans; correct plans should be within the 10% slop.