"Are kit built Thompson Renegades worth about the same as factory built units as long as they were assembled/finished correctly?
Can I assume a “K” prefix to a SN means it was a kit? "
Let me answer this again. IF I assembled it today, it would be better than factory. The fit, finish, styling and mechanical operation would all be superior to factory. However, most of them were assembled by beginners who did not know what they were doing. The one I assembled at age 14, was pretty sad. Each rifle will need to be judged on it's own merit.
Toward the end TC was using hot glue to bed the barrels. What was that about? It does not matter today, TC kits have been gone for 30 years.
TC-SW warrantee???
This warranty is granted by Smith & Wesson Corp. doing business as Thompson/Center Arms. This warranty is effective from the date of purchase for the lifetime of the original retail purchaser of any factory finished firearm. In order to be eligible for service under this warranty, the original retail purchaser must return a completed authorized warranty card or
REGISTER ONLINE within thirty (30) days of purchase of such firearm. With respect to such firearm, this warranty supersedes any and all other warranties.
Since you can not meet the terms with your old TC ML you are s.o.l. on any "lifetime warrantee". The TC that made the rifle no longer exists.