Tom, You never seen Freund?? spelling? Pricision replacement parts still in bag with mfg dates on them like OP's.. Earliest I believe is 1979 and latest was 1983-84. Thought with all the furniture you go thru, funshows etc. you would have seen plenty of them. Freund?? plant was in your neck of the woods. They were govt contract to replace the broken stuff and possibly OEM also. Not uncommon or wasn't back then to use existing available inventory instead of trashing. IThe equipment they used probably same stuff from early Colt sub contract truth be known, but I honestly don't know on that. Pretty sure Lionel still has some Freund Precision HG's NIW with 80's dates on them. Stocks weren't as common. I've seen plenty like OP's not many like one in my picture. Got a few on personal stuff and a few members contact from time to time showing theirs.
H&R's were done same as old type C an earlier as you mentioned. . Might still have some dated bags from HG's laying around with just don't know where to look right off thinking HG's have letter or number by heat shield. Don't have any to look at all have been used or sold.
H&R marking pic. Never had a Freund stock NIW but have had NIW Freund?? mfg PG's, A-1 with 1980's date on wrap. Never paid any attention to markings. All my H & R's are no straw hole type D and type E.
With a little more thought the Freund?? numbers and letter from late 70's- 80's aren't as crude as OP first example IMO. Freunds' had nice and sharp letter / numbers like new molds were used. Added more insight couple posts down.