Pt6 vs Garett, itt vs egt
 

Why is it that the ITT limiting temperatures for a typical pt6a say -34 does not change with oat? In a Garett without SRL and TTL, you have to work out the limiting egt for the corresponding oat.

Is it because the limiting factor is turbine blade creep temperatures where ITT is almost directly measuring this and EGT readings have to be combined with oat to find that limit ?