Older ones were made in West Germany or Germany. Newer ones assembled in N.H. Older ones have no rail, new with R on the end have a rail.
Newer ones have MIM parts. Military ordered new 228's a year or so ago for their invetigators.
I have W. Germany made 228's and love them.
Should be a date code on the bottom front of the slide. From that you can determine the date made.
The newer pistols have date codes such as "KA" or "KF" . If memory serves me correctly, K= 9, and
A=0 meaning it would be a 1990 built pistol.
Also You might remove the grip panels for further examination, and see if you find a date code inside. It might have something that looks like a clock, with an arrow pointing to a particular number; and having a two digit number in the middle. If so, the number that the arrow points to is the month the weapon was made; and the two digit number in the middle would be the year.
And finally:
German manufactured SIG-Sauers typically come with three proof marks. The first is an ornamental crown with an N beneath it to indicate it was proofed with smokeless (nitrocellulose) powder. The second looks like a "squished 8-legged 2-pincered bug". This is the proof mark for the Kiel, Germany proofhouse. Lastly, the proof house adds a two letter code to indicate the year the gun was proofed. The table shows the letter to digit mapping. For example: a SIG-Sauer stamped KB was proofed in 1991. One stamped JJ was proofed in '88.
A = 0
B = 1
C = 2
D = 3
E = 4
F = 5
G = 6
H = 7
J = 8
K = 9
The above is partially correct. The date inside the grip panels has nothing to do with the pistol, it just indicates when the grips were made.
P228s come in four main flavors: all German, German made but US assembled, SAS (SIG Anti Snag, factory dehorned), and the P228R made from German slides and railed P229 frames.