I Have two M-4506 autos, which - if I remember correctly - were purchased from LAPRAC in the mid 80's. They are marked as follows: Model 4506, have the round trigger guard. The s/n are TDR 3293 and TDR 3372. Are they 4506-0, 4506-1, etc?
If i recall correctly the TDR prefix was mostly 1999-2000 vintage which would make them late 4506 after they stopped including the dash numbers. For Example 4513TSW 6rd TDR302x dates to December 1999. 4513TSW 7rd TDR744x dates to January 2000.
The tell would be the frame. The early 4506 no dash had stepped frames with D shaped trigger guards while the 4506-1 frames were were thicker and non-stepped with curved trigger guards and were marked 4506-1 on frame.
The last and potentially most desirable 4506 frames (box ends marked "03") circa 1998 were no longer marked with dash numbers but were essentially the same geometry as the 4506-1.
My guess is the TDR prefix and curved trigger guard you have are the last variant circa 1999.