A comparison of these two words may have been discussed previously however I cannot locate the place. These words are generally held to be synonymous, both sharing ‘ssagga’, however the contexts of use in the suttas appear to be different.
‘Vossagga’ appears to be used in the development of meditation (eg. SN 48.10 developing concentration; MN 118 developing factors of enlightenment) or in the surrendering of social authority or privilege (eg. DN 31, to wife & to employee). The dictionaries provide meanings such as ‘giving up’, ‘relaxation’, ‘handing over’ or ‘surrender’.
‘Paṭinissaggā’ appears to be used with the completion of the path, such as the 16th stage of anapanasati (MN 118), 3rd noble truth (SN 56.11) or description of Nibbana (AN 3.32; MN 26).
enclitic from tumha
to you; of you; by you
Vo˚ is commonly regarded as the prefix combn vi+ava˚ (i. e. vi+o˚), but in many cases it simply represents ava˚ (=o˚) with v as euphonic (“vorschlag”), as in vonata (=onata), voloketi, vokkanti, vokiṇṇa, voropeti, vosāpeti, vosāna, vossagga. In a few cases it corresponds to vi+ud˚, as in vokkamati, vocchijjati, voyoga.
relaxation, in cpd. sati-ossagga (for which more common sati-vossagga) relaxation of memory inattention, thoughtlessness Dhp-a.iii.163 (for pamāda Dhp.167). See vossagga.
Vossagga [=ossagga; ava+sṛj] relinquishing, relaxation; handing over, donation, gift (see on term as ethical Bdhgh at K.S. i.321) D iii.190 (issariya˚ handing over of authority)
Nisagga (& Nissagga) [ni or nis+sṛj] giving forth, bestowing; natural state, nature S i.54 (˚ss˚). Cp. nisaṭṭha.
directional prefix in well-defined meaning of “back (to), against towards, in opposition to, opposite.”
I once read ‘paṭinissaggā’ means to 'give back the things wrongly attached to as self’.
Seeking any compelling scholarly or linguistic insights into these terms.