Soloist neck joint/heel variations mean year association?

[wyldwulf]

I've been shopping for a 90s era Soloist. The heels are all over the place and based on the years posted there doesn't seem to be much consistency. Were these mixed and matched? It doesn't seem to matter in import or USA, they vary and don't seem to be chronological. The one that has a crescent shape scoop below the neck joint similar to many Dinkys look like they might be thinnest- can anyone shed light on the variations? The one consistent factor I see is that the earliest ones seem to have the most extra wood at the heel in the form of a hump.

Thanks in advance!