After re-reading GoO i find it highly possible that the lone wolf was a Spartan III that survived Pegasi.
Now we know for a fact that the lone wolf is a spartan III based on the Pegasi reference. but the only known survivors were Tom and Lucy.
My theory revolves around page 14 in GoO in which immediately after the drop on Pegasi Tom notices 9 Spartan III's are missing and believes them to be KIA and moves on without a care.
Funny how that was overlooked right?, now here is the hypothetical situation
"The Spartan III in halo reach could be one of the 9 Spartans that weren't found right after the drop. for all we know he/she could have done a solo op and then returned to the exo craft to later be picked up by ONI and listed KIA. the Spartan would then preform LONE WOLF operations for ONI specifically."
To further support my claim remember when Ackerson asked for Tom to Put under his command? The same deal could happen with our Lone wolf, seeing how he/she was one of the few to survive she/he could have been placed directly under an ONI spook until the battle of reach.