ZAB Controller reported URET did not retain data on an IR aircraft. When the aircraft was ready to return to base the Controller was surprised as he had no data.

Narrative

After sitting on R23 for a short time with no significant workload; I receive a seemingly random radio call from Aircraft X stating he is exiting IR-194 PT U and requesting to return to base VFR. I had absolutely no information on this aircraft. No information visible in User request Evaluation Tool (URET); no strip on sector; and I do not recall the relief briefing discussing aircraft in the route. There were no other visual cues that indicated to me there was any activity in the route. I asked the adjacent sector whether they had any information on the aircraft; and they stated they had information in URET and were protecting for the aircraft as necessary. I rate the severity of the situation as major despite there being no other known traffic in the area as; if there were low-level traffic in the vicinity of the exit point (which does happen often since traffic circumnavigates the eastern side of R5103B/C); there was a very high potential for this aircraft to climb directly in to traffic with no prior warning. Had an accident occurred; I may never have been aware of the Aircraft X's existence. The fact that I had no information showing in URET is most surprising. I often work traffic in this IR route and regularly use URET to maintain aircraft identification throughout an IR route. While required by our local SOP I admit to not normally using strips to keep track of these aircraft as URET is usually more than sufficient. This was not a factor in this case though; as I sat on sector after the IR route was already active; and there were no strips on sector to begin with. My suggestion would be that URET aircraft information for IR routes remain persistent in URET for any sector the IR route affects from the time the aircraft departs. Especially in the case of IR routes like this that enter and exit in the same sector; there should be no reason URET would lose flight plan information; even if the datablock is handed off for flight plan processing purposes (necessary for IR-194 and ZFW). Perhaps flight plan processing will improve if/when ERAM is ever implemented; but there still seems to be an issue with this IR-Route and us having to flash a non-radar datablock through ZFW to ensure full flight plan processing.