reg number question

I have pics of this same exact plane. the tail number is 86039 but the reg number is 18-46039
I don't understand why the numbers don't match. when i go to caption my photos i want to do it right.
So how do i know the tail numbers on the ADSB Exchange panel?
https://www.planespotters.net/photo...ates-air-force-boeing-kc-46a-pegasus-767-2lkc
here it is on the map. https://globe.adsbexchange.com/?icao=ae5f92

 

anyone? where is everyone? this forum is been quiet for the last few weeks

 

Here's what "little" I know.
18-46039/46057 Boeing KC-46A Pegasus
Boeing Model 767-2LKC
46039 (MSN 34089/1160/VH039) Registered as N1785B. First flight 20Apr19. Delivered to USAF 9Aug19.
344th Air Refueling Squadron, 22nd Air Refueling Wing, McConnell AFB, Wichita, KS. Active 9 Aug 2019 Sep 2019

18 is the Fiscal Year. It is important to recognize that the serial number reflects the Fiscal Year in which the order for the aircraft is placed, NOT the year in which it is delivered.
46039 is the Serial number. Serial numbers are 5 digits. What they paint on the tail is not the full number.

This page is a good source of info for the numbers: http://www.joebaugher.com/

Hopefully others can add or correct this info.

 

but the number on the tail doesn't match the full number. I don't get it.

 

And it usually will not. Some explanation of the display of the numbers on the tail is provided here: http://www.joebaugher.com/usaf_serials/usafserials.html scroll down to the paragraph titled The Display of Serial Numbers on Aircraft
In your case, with a little detective work, the tail display is the last digit of the year plus the last 4 of the serial number. I agree, it is confusing.

For example on the confusion, I caught a C17A Globemaster III at KCLE. The tail number is 23291. Took a while, but the leading 2 is for the year 1992. The 3291 is the serial number. In this case it is only 4 digits, not 5 (ie, 92-3291 vs your spot is 18-46039). So very little consistency but with a some work, you can resolve what the full serial number is; but that full number is not generally displayed on the tail. The previously mentioned website can be a good source to decipher the tails . I am hoping others can chime in and provide better info!!!