That would seem odd for the NRL to demand that your Top 30 be filled before you can request an exemption.
Very few NRL top 30's are filled at this time of the year and aren't required to be filled until June 30.
Brent Woolfe played for the dolphins in round 1... debuting at 28yr... did they really sign him to a development deal or top 30 contract for that one round?
A quick google has him quoted as being T&T and the NRL contracts page has them at 28 players.
NRL contracts is a shit page that can never really be trusted, but the previous explanation of requesting exemptions was that you had to prove you had no players for that position within your top 30.
That doesn't necessarily mean there's a caveat that your top 30 also needs to be filled, just guys that have a "Top 30" level contract.