Just because I was thinking about it, let's recap where ATSG is with its officially-contracted additional 10 more aircraft for Amazon, and look at that in light of the 20 ex-AA aircraft that ATSG/CAM has optioned and the two ex-DL aircraft that it has now purchased.
The 10 Amazon aircraft will be delivered 5 this year and 5 next year, according to the press release about the agreement.
Of the 5 aircraft to be delivered this year, one is already in service with ATI and being used on other assignments for now (382CM, to be 389AZ, formerly 930WE).
Another is done with conversion but not yet flown back from TLV (730WE, to be 367AZ).
A third is in conversion now, to be completed in August (354AA, to be 397AZ).
So at-least-three of the 10 for Amazon will be completed without even beginning to dig into the 22 reserved feedstock.
And in fact, all 5 needed in 2019 could be provided from existing or in-conversion aircraft, although apparently they won't be:
N830WE is at TLV in conversion, to be done in September, which may or may not go to Amazon. And the two other ATI aircraft currently in use for UPS could also be available, although it appears they will be used for something else (376AN to be 344CM, and 373AA to be 359CM).
That would be five. Assuming that those three will in fact go somewhere else, that leaves ATSG with a potential conversion pool of 19 aircraft after plucking out 3 more for Amazon this year, or 20 aircraft after plucking out two for Amazon this year. Only 5 of those 19-or-20 are currently-slated for Amazon next year, leaving a pool of 14 potential conversions over the next three years that will be available to dry-lease or to use to service other ATI, ABX and OAE business. That's a bunch. It will be interesting to see where they go. Given UPS's apparent interest in converted 767-300 freighters, some could be dry-leased to UPS on long-term leases. Although nobody has said it, that may be where those two aircraft that ATI is currently flying for UPS could be going. There was talk that two currently-converted aircraft would be going to "a major integrator", and it apparently is not DHL, because ABX isn't getting any new 767s and typically DHL has used ABX as opposed to ATI for 767 flying; the ABX pilots will poop giant bricks if ATI starts flying two 767s for DHL. There are certainly non-household-name significant integrators that they could be talking about, so it will be interesting to see.
In terms of potential tail (prime) numbers starting with 3, there are six left: 367, 373, 379, 383, 389, and 397. We know about 389, 367 and 397. That leaves 373, 379 and 383. Also, there were a couple missing from the original series: 317 and 349. 349 is now available (it was assigned back then), and 317 has always been available. CAM has reserved 379AZ, but 373 and 383 are presently assigned to other aircraft. Doesn't mean someone can't make a deal for those numbers if they want, but we will see.
So at least two of the 10 aircraft will have tail numbers other than 3--AZ, and maybe more.