Mass Effect 1: Single playthrough builds (by Simbacca)

I agree!!!

That's right.  It should have unlocked at 260, but did not unlocked until 278... And, I've got more bad news.  My total paragon after Feros and talking with Udina about it on the Citadel was 249.  I just did BDtS and collected 26 Paragon only (24 for letting Balak go and 2 when talking to Simon Atwell afterwards), which brought my total to exactly 275.  Guess what, Besieged Base has not unlocked... and I sincerely doubt I missed 2 paragon as well.  I know absolutely that I gave Tali her data for that single point.

For my next trick... I'm going to make a botched run at Virmire... trying to take only 2 paragon points in total.  If the mission unlocks, the magic number on the Xbox would have to be 277 (trusting that I made no errors on the renegade side).  This is certainly not going as I expected it.

ETA:  Besieged Base did not unlock, even at 279 paragon (i.e. getting 4 more paragon total on Virmire).  Will try going back to just after BDtS and do The Negotiation in a paragon way to add 8 Paragon and bring the total at that point to 283.  Failing that, I don't think there's much more I can do without some additional Charm points that I just don't have available)... I'll look at it closer when I'm less tired.  (IMO - Using the Lorek Qui'in glitch is certainly the best way to go on the Xbox to ensure that everything unlocks.)

ETA2:  Belay all of the above re paragon... I just found my mistake... wrote in an 8 in  the paragon column that is a complete accident (no dialogue associated with it).  Will adapt by doing one of the two remaining side missions I have that adds 8 paragon and will get back to you tomorrow.  Will eventually attach the spreadsheet for you to verify.