$3.85 Jefferson Memorial Stamp I Can't Identify

i have a $3.85 jefferson memorial stamp that I have found 2 numbers for. SC# 3647 and SC# 3647a.

3647 says it is a perf 11.25
3674a says it is perf 11 x 10.75

The one I have is at best a 11 x 11.25
(I'm a newbie to this so 11 is the vertical on this stamp and 11.25 on the horizontalk)

I got my info frome Stamp Smarter and Mystic Stamps.

Thanks in advance for help,
John

Is there another one I am not seeing as a possibility?

You can check the date in the lower left corner. 2002 is 3647 and 2003 is 3647A. As a newbie I will mention to you that "A" and "a" are different beasts. The capitol letter after the number means the number with a letter is a fully different stamp. A lower case letter indicates as minor (sometimes significant) variety of the numbered stamp.

Edit:

While I, as a collector, lived through the issuance of both, with the date issue well mentioned, the information is contained in a footnote listing after the stamps in the Scott US Specialized Catalog. I mention this for those who own the catalogue as well as for others to understand some of the information pearls contained in the catalogue.

Yes, I found those 2 listings 3647 and 3647A (sorry my caps was off). But what about the perf discrepancy?
3647 says it is a perf 11.25
3674A says it is perf 11 x 10.75
The one I have is 11 x 11.25 (and I measured multiple times).

Perf numbers are rounded. The date, 2002 verses 2003, tells you what perf. If you have two 3647 turn one on edge and line up the perfs.

Edit:
Normally such questions are accompanied photos of your stamp and a perf gauge.

Perf measurements are usually given as horizontal x vertical. If only one value is given, then the assumption is that the horizontal & vertical gauges are the same. Note that, while highly unusual, it is possible for the gauge to be different on all 4 sides of a rectangular stamp. In this case the perfs are reported as follows: top x right x bottom x left
You also need to be aware that Scott tends to round perf measurements in increments of 0.25. I used my Scott multi-gauge to measure the perfs on both of these stamps. This tool can measure the perf gauge in tenths. I won't promise that my aging eyes got the results exactly right, but they should be extremely close.
3647 ... 11.3x11.2
3647A ... 10.8x10.6
As to be expected, Scott reports 3647 as perf 11.25. But 3647A is a bit surprising as I would have expected 10.75x10.5 ... or maybe even 10.75. Perhaps my measurements on 3647A were off by a tenth in one or both dimensions. In any event, 11x10.75 can be seen as a relatively logical result.
Note that if there is the possibility of confusion when there are multiple perf values for the same design, Scott will forego the rounding.

Hi again.
My eyes must be playing tricks on me. I measured that stamp 10 times yesterday and each time came up with 11 x 11.25! Today I measured it and it was clearly 11.25 in both directions. I think my cat stretched the 11 last night while I was sleeping, LOL.
Thank you all for your help.