Pitru Paksha is the fortnight given to the ancestors. For those fifteen days the pitrs are held to come near, and the household offers tarpan, pind daan and shraddh in their names. It is not a remedy taken for oneself. It is a debt acknowledged, the pitru-rin every family carries whether or not it is named.
The Special Pujas below are performed on a tithi you choose rather than on a fixed festival date, so a shraddh tithi that falls outside the fortnight is served just as well. Each is carried at a kshetra prescribed for the rite — the Siddhvat at Ujjain where Mata Parvati is held to have first offered tarpan, Vishnupad at Gaya, and the ghats at Varanasi.
7 sevas at 6 Teerth Kshetras — you choose the tithi.
The sevas here are performed on a tithi you choose, so they are not tied to the fortnight. Shraddh on the departed's own tithi, and tarpan on any Amavasya, are both accepted practice. Sarva-pitru Amavasya is taken when the exact tithi is not known.
The 7 sevas here are Special Pujas — you choose the tithi yourself at checkout, so they are available year-round and are not tied to a fixed festival date.