Yes, it is probably the best site as it uses original documents. Unfortunately the Air Force Museum fact sheets it refers to have been moved and possibly removed.
The XA-26D on the page have aircraft cards, dates and photographs.
The XA-26E on the page has no aircraft card, no dates and no photographs. The page provides no evidence of existence.
The time between the airframe becoming available and the XA-26D conversion done is given as about 6 months. Using this time interval the XA-26E, factory completed in April, would have become available in October 1945, post war, also in May the A-26E order was at least temporarily dropped.
The list of USAAF contacts has XP-26E 44-35563 as a cancelled contract while the reported XA-26D serials are under A-26B.
Original Contracts AC-21393 for Long Beach (495B, 5 C), AC-34433 for Tulsa (205 B, 295 C)
J program (approved June 1943) contracts AC-21393 SA.13 for Long Beach, AC-34433 SA.3 for Tulsa, serials Long Beach 44-34098 to 35197, total 1,100, Tulsa 44-35198 to 36797, total 1,600. RC-301 reports (Completion is month production is expected to end)
Aug-44 Long Beach 1100 B completion Oct 45, Tulsa 1600 C completion Aug 45
Dec-44 Long Beach 665 B completion Jul 45, 435 D completion Oct 45, Tulsa 1600 C completion Aug 45
May-45 Long Beach 665 B completion Aug 45, 435 D completion Dec 45, Tulsa 1253 C completion Dec 45
Jun-45 Long Beach 955 B completion Nov 45, 145 D completion Dec 45, Tulsa 153 B completion Dec 45, 1100 C completion Sep 45
K program (approved June 1944), to December 1944 the A-26 are listed as further supplements to the original contracts, from then on Long Beach is contract AC-5141, Tulsa 2000 AC-5140
Aug-44 Long Beach 400 B, Tulsa 2000 C, both completion Dec 45
Dec-44 Long Beach 400 D completion Jan 46, Tulsa 2000 E completion Mar 46, same month as D models appear in the J program order.
Jan-45 Long Beach 400+350 D, AC-5141 + SA.6, completion Apr+Nov 46, Tulsa 2000+1250 E, AC-5140 + SA.7, completion Apr+Aug 46
May-45 Long Beach 400+350 D, AC-5141 + SA.6, completion Apr+Aug 46)
So in May 1945 the Tulsa C contract is cut by 347, leaving 700 to be accepted, and the E contract is dropped, I am unsure if it was a temporary or permanent change, a month later 143 Tulsa C models are changed to B. Which makes it look like the USAAF felt it had enough bombardier nose A-26. The reduction in the number of D models in the J program order also indicates the D project was experiencing delays, plus the expected completion date changes, though the general run down of aircraft production in the US was also a factor.
All the above means even less chance the XA-26E ever flew.