Firstly i must say, this is a very nice patek.
i always liked model 2552, and being Wg or Pt just makes it even better.
As ref 2552 uses the same movement as ref 2526,
around the same time period, late 50's
i am thinking ( purely ) in my own opinion,
could it be around the same as ref 2526 ??
According to a very famous auction house,
patek 2526 was around 580 pieces
mostly yellow gold, small number of rose, WG and PT being the smallest production number.
the given information may apply also to your 2552.
What do you think ?
By the way, in your second picture,
i dont know if its the photo or something,
at the back, under the top two lugs,
is that a small dent, scratch or hole ??
A very nice watch to keep for the next generation.