An entirely different ship... As far as I recall, the Lex in Armada is a one-off heavy carrier with extra equipment to set up mining stations and fighter plants etc...
The Lady Lex we see in WCIV is a Concordia Class fleet carrier, recently commissioned but nothing special...
Now here's my quabble. If a ship is only presumed to be MIA, and not certainly KIA, why assign its name to another ship? I mean suppose the Lex would jump into Sol tomorrow...
Also, in Victory Streak one of the squadrons who triumphed at the GCM competition was based on the TCS Lexington... Since VS is written in 2669.220 and for other reasons I will disregard this as being the Armada Lexington... So is it the WCIV Lex, or was there a ship inbetween? And if there was, how in the MrKat did they fit all three into such a short period of time?