The flat spacer strips without letters can be literally any sort of lead alloy. I had a couple of batches once where the alloy was lead/tin, some that were nearly plain lead. But the holy cow win for me was several buckets of spacers that XRF gunned as better than linotype.

Rule of thumb (for me) is if it has letters keep it in that form, it is like a silver dollar or silver quarter, you know exactly what alloy it is because it is linotype, or monotype, or foundry type which can be distinguished from each other and are a known alloy. Strips that are just spacers however I go with the big batch for a consistent alloy approach.

I do Dutch oven sized batches of around 100#, poured into bread loaf pan molds to make approx 1" slabs of around 12 - 16 pounds. I keep each pot sized batch separate and label the slabs from a single pot with "A", "B", "C" and so forth. Then once done I take same number or weight of slabs from each letter labeled batch to re-melt into a blend of all the pots. So instead of having 3 100# batches of mixed spacers that might be different I cross mix 35# from each batch so in the end I have 300# of identical lead. I then get that tested either at scrap yard or by member BNE here on the forum.

It is extra work to cross mix the ingots from multiple pots but in the end I think it is better to have those "unknown" strips all converted into a big supply of known and consistent alloy. The different batches of mixed strips kept separate could be wildly different depending on what sort of strips were in each batch. You can of course test batches A, B, and C to see if they are already the same and possibly avoid the extra step.

I started doing this because when I scrounge scrap I could estimate it was good lead based on form, hardness, melting characteristics but a lot of times I would have a little of this, and a pile of that and some of this other stuff. Big batches are consistent alloy, even if sometimes sort of odd combinations. I have one that is 1.5 times linotype. Not sure what it was in that print shop scrap barrel that kicked it to that but don't care, good alloy.