I think Alan was correct with the "Caithness period PY" attribution for Lot 511. And I believe Lot 510 was probably from the same era. But a check with shortwave uv is the only way I know to prove it.
Lots 510 & 511, being unsigned PY, may originally have had a Caithness Glass label.
Lot 510 is interesting to some collectors because of the left-facing fish, which is (so far) less common that right-facing ones.
The Lot 513 Butterfly is of interest because of the two "PY" canes (which tend to push prices quite high when the weight is not damaged). But also of interest to me is that, of the few PY Butterfly weights with two "PY" canes I have seen, at least three have been very similar in appearance ... Mottled pale blue ground with butterfly mainly formed from yellowish coloured canes and the butterfly having red aventurine body with white antennae tipped in red.