Can Someone Shed Some Light?

Agreed.
Gibbons did there part by acknowledging it
Obtaining the reason for it if any may take some time
Perhaps it's not represented with a explanation so Scott's doesn't list it
I'd like to hear if the C.S.S catalogue lists something?

I've got nothing but time now.

Britain recognised the Peking government in January 1950. As far as I'm aware, aside from some export controls on military-related equipment, Britain didn't restrict trade with China after 1949, although trade wasn't, in any case, significant.

Hi

I have the CSS Catalog published 2021. Couldn't locate this stamp in the catalog:

Maybe a email to them with a photo of the letter might lead somewhere?

The CSS catalog is Imperial/Republic of China stamps, so I am not surprised it isn't in there. This stamp is a PRC usage stamp from the NE region and is listed in the back of the PRC section of the Scott catalog and I would assume that same in SG.

Hi Percyjpg thanks for jumping in
a while back you helped me with this if I remember right it was a 3L60 (Scott)
pretty sure it's a nc300(a)(grey think they added it) in gibbons

Sounds good. I figured it was in that section. Either 3L49 or 3L60 in the Scott catalogue, but neither show a grey overprint, so it is possible that Scott doesn't recognize the variety and Gibbons does. The CSS should still be able to help. You may be able to just email a good scan to someone there to get a positive ID on it.

expertizing@chinastampsociety.org

Thanks!
Appreciate the help again
Might be worth sending a message just to ask there opinions

I'd like to thank everyone who has taken the time to assist me with this identification. I'll definitely get in contact with CSS to seek further guidance before contacting Stanley Gibbons.

Keep us posted :)

I will. This stamp has given a a good reason to take a closer look at my worldwide collections.

Terrible Thread Title.
Opinion.
"Just Fella" had it right, first go.

Oops! was going off first scan
Time to re visit

NE Provinces SG Type 5 or Sc# Type A2
25c black brown
Dr. Sun Yat Sen

No similar Opt listed, It is the character left of the Dr's nose
that differs from the SG listings.
(SG Opts types NC73 and NC74)

This may be covered by Gibbons note.
"On these stamps, the bottom character in LH column is square in shape"

Alas! that covers Type NC74 opt, not NC73 which would make it perfect.

The nc300(a) is type nc74
Nc73 reads "changed to"
Nc74 reads "temporarily"
Right hand characters

CORRECTION --To my posting ,first your copy is 3L49 in Scott Catalog it has the grey/black overprint and is catalog at $9.00 mint .

My copy is 3L60 with the green overprint and catalogs at .50 cents ,I don't have a copy of the 3L49 . These are called Northwest China in most Western catalogs but in China the are just North China.