US Special Delivery Scott # E4 Or E5

Is a watermark the only way to tell the difference between these two special delivery stamps? I looked in Scotts and StampSmarter and saw the watermark as the only difference or did I miss something?

I have a few on cover and the price for the E4 is $110.00 used and $300.00 on cover.
The price for the E5 is $12.50 used and $25.00 on cover.

If this is the only way, then do I remove the stamp and see if I have the E4 and a $110.00 stamp or the E5 $12.50 stamp? Or keep them on cover and not know which they are?
Thanks,
Bob

Does the cover date lend any additional information (compared to issue dates of stamps)?
Don

The postmark on one is 1902 and the other is not legible.
Bob

Date makes E5 a bit more likely. Is the cover from a larger or smaller PO? (Having the cover image would be helpful).
Don

When I saw 1902 I thought E5 also. I will post scans tomorrow.
Thanks,
Bob

Here is a direct answer:
1. Watermark
2. On cover or piece use where the dated postmark (of E-4) predates the issuance of E-5.
3. The so called "DOTS" of E-5 Plate Number 882 (E5a).
4. Line through "Postal Delivery" variety of E-5.
5. Any stamp with selvage including a plate number other than 77.

#3 and #4 do not occur on E-4.

#5, Plate 77 was the only plate used for E-4, but was used for E-5 as well. Any other plate number used on E-5 is not found on E-4.

Wow such great information. I am going to scan the covers later.
Thanks,
Bob

Here are 3 covers I have. It looks like two dates 1902 and 1 dated 1900.

1 - Watermark - Cannot see because on cover
2 - The postmarks are 1902, 1902, and 1900 so technically it could be either
3 - No dots so it could be either
4 - No sure what the lines through Postal Delivery looks like so not sure
5 - No selvage so could be either

Does anyone have a scan of the E5 with the line through Postal Delivery? That may help. Also, I wonder if I put watermark fluid on the stamp would I be able to see a watermark if held up to a light.
Thanks again,
Bob

Few Years Later..... .... ... .. .

Here is a scan of an E5a , it has the slightest hair line going through the closer to lower middle of the words Postal Delivery.

Bob, I know it's been 3 year, but if you could correct "2 - The postmarks are 1902, 1902, and 1900 so technically it could be either."
... since it's easier to edit than disturb the images posted previously! (2nd image is of 1900, not 1902 3rd image is of 1902, not 1900.)

I've faced your dilemma more often when it comes to postal stationery, watermarks and usually result to a bare light bulb "inside" an opened envelope.

Note that one never disturbs a stamp in a high-$-value situation on cover, until getting a certificate first that will judge that the "stamp originated on cover." Then the stamp can be removed for watermarking if it comes to that.

But I just had a new idea, to improve on your chance of using a strong light source behind the (layers of) paper ... obviously you need a setup where (for instance) the cover is flat on a piece of glass positioned high enough for light source to be placed below glass, so you can put proper amount of watermark detection fluid on stamp. My suggestion is, the envelope flap(s) could be carefully separated, so that only one layer of envelope paper is "blocking" light source coming up through the stamp (and watermark fluid). This would preserve having stamp undisturbed still on cover (care must be taken when separating the flap in area behind stamp, that whatever is used to loosen the flap gum/glue does NOT reach stamp ... like putting a piece of plastic in that corner behind the envelope paper plus stamp area).