identify correct balance

I have a rental with vinyl windows installed 10-12 years ago. The balances installed have 18 3 BS1 stamped on them. I cannot get them to engage properly, the tail end of the balance always sticks out past bottom of window. It has been a while since this window has functioned correctly.

Overall window length is 19 5/8, with a 1 1/2 inch setback to where I think the top of the balance should be. Any thoughts? Does an 18-3 sound right? Just looking at it (and I have pulled/reinstalled other balances so I don't think its misapplication of correct hardware) it seems kind of long, maybe should be a 16 or 17 inch. ??

So regardless of length, can you tell me which type to order to get replacements? I.E, 19-002, 15-004, etc? Thanks