Autopush should be obvious and history should be compared to new retrieved data, so every missed entry while abz was closed won't be missed.
RSS before closing abz:
R3
R2
R1
RSS after starting abz and manualy refresing feed:
R5
R4
R3
R2
R1
and you press Timer R4 and R5 will be lost for autoprocessing and my suggestment is that with RSS Autopush R4 and R5 should be evaluated with RSS filters.
