The way I view it is the extra two weeks is to extend your prospects, either to a regular extension or a prospect extension. And that is the way the rule is worded. So if someone else from the RC would like to chime in please do so.
Not sure I am interpreting the following which is the wording under prospects extensions under contracts in the rules.
There is a window after the season in which the multipliers above are still in effect. This was a rule effective June 16th, 2011 for expiring prospect contracts.
Prospect extensions on expired prospect contracts will be the only type of extensions allowable for expired contracts in the offseason. Therefore, after the 2011 regular season is over, a P-2011 contract is still eligible for the prospect extension at the 2011 rate. This window for prospect extensions is open until one week prior to the beginning of offseason free agency.
When I read the bolded line it clearly states that
PROSPECT EXTENSIONS on expired
PROSPECT CONTRACTS are the only type of extensions allowable in the offseason. To me this would mean that an expired contract needs to be extended using a prospect extension and not a regular extension.