I think you have to consider a number of variables here. No you shouldn’t have been supplied with a substandard item, however when you consider that Rimmers & other supplier have been far sighted enough to lay in redundant stock for a long obsolete engine, it shouldn’t be a surprise if irritations arise.
You should be able read the manufacture date from the “dials” molded into the inner surface. I don’t have an example in front of me at the moment as I’m sat in front of a roaring fire looking out on a below freezing garden & that should convey why I’m not going into either the workshop or garage to collect a suitable piece of plastic.
The dials will tell you the year of manufacture, the month, day & machine used, this for “quality control” purposes.
From then on it’s up to how the item is stored until the picker at Rimmers chose your item.
If during its lifetime it has been stored with a slight bow, that bow will have been “memorised”, warming it up to its plastic state & applying a reverse bow will in all probability correct it.
Voice of experience. M