Digital BW, The Print

On this subject, I looded at archival data from Wilhelm's site one  
for prints made on the 9800:

http://www.wilhelm-research.com/epson/9800.html

and the other for Hahnemuhle papers printed on the 7800 (data should  
comparable):

http://www.wilhelm-research.com/WIR%20Hahnemuhle_2008_10_20%20/ 
Hahnemuhle%20Inkjet%20Papers.html

and found something very interesting:

Premium Luster 250 (OBA's and RC) rated 71 years under glass, 165  
under UV, 48 with bare bulb and >200 in dark storage.

Photo Rag Pearl (no OBA and Rag) rated 64 years under glass, 126  
under UV, 35 with bare bulb and >200 in dark storage.

With the recent discussions on OBAs and paper bases, how is it  
possible for Premium Luster to last longer? Not only that but:

Fine Art Pearl (OBA's and Rag) rated 82 years under glass, 148 under  
UV, 46 with bare bulb and >200 in dark storage.

So of the two Hahnemuhle papers, the one with OBAs outlasts the  
"purer" paper.

Am I misunderstanding something?

Thanks!

Jim