Hi,
There was Constantin Yakovlevich Petz (Константин Яковлевич Пец) in Moscow, working at the time when your basket was assayed.
More marks are expected (handle, basket sides).
Regards
Curiously,though, there was another mark overstruck with maker`s mark, whose name is written in old orthography (mentioned in PL book).
As said, search for more marks, possibly only 84 and КП.
2nd mark set is visible on outside of handle in upper photo, but not readable. Can you confirm 84 in square cartouche and repetition of same ovalesque maker mark shown in your second photo?