Can dissipation factor (DF) for electrolytic capacitors in any case decrease from initial reading after undergoing Endurance test for 2000hrs (ALT at 105C)
All other parameters are kept constant (temp & frequency )
Not really - as you heat up the cap with either AC current or ambient heating the DF falls as the electrolyte is more " active " if you like, at elevated temps.
There is also usually an elevated AC current rating for frequencies in the 1kHz - 50kHz range due to properties of the electrolyte which are as yet not well understood.
Above 50kHz ( lower for some ) the capacitor is inductive