Regarding depositions, I am much in support that one jurisdiction should not accept as clergy those defrocked by another jurisdiction. However, there is an exception to this if the defrockings can be shown to be unjustified or based on erroneous reasons. This requires the proper investigation of a council. The case of the Antichocian Priests may come into this. However, I get rather upset when a jurisdiction that recognises another as valid accepts a Priest who was defrocked for immorality or clear schism. This does no good whatever to harmony and respect.
Some Old Calendar groups denying grace in “mainstream” Orthodox jurisdictions are free to do as they please because they do not see a valid ordination anyway. Nevertheless, some candidates that seem to have made their way into these bodies are of dubious quality and don’t add credit to these bodies; not to say that all clergy in mainstream Churches are beyond dubiousness.
Within Orthodoxy there seem to be two developing camps in the Church regarding relations with other churches and the opinions dividing these camps are reflected on their attitudes to receiving converts, especially from Roman Catholicism and these camps focus on what are acceptable rites rather than on error or validity per say. Those who see the Roman Church as being a genuine Sister Church should not accept converts but rather encourage people to stay with their own pastors and should be opposed to the Orthodox presence in Western countries anyway to even permit free attending; on this reasoning Eastern Churches have no place in the west unless one does so for ethic reasons but these parishes should still be under western Bishops. Most Orthodox Churches in the West do not officially fall into this category and this presupposes that the Roman Church or other western churches are not legitimate churches but rather in error. Whether this error only requires confession or whether it requires baptism is another issue. Even though only chrism and confession is permitted by conciliar decision in the US, such a position is considered erroneous on Mt Athos, who see it as endangering souls who have not been baptised in a manner acceptable to the Church. I understand the main Orthodox issue being that the Roman form of baptism is not baptism but sometime different and as such cannot have any validity at the time of application or upon reception into the Church. Even if it was accepted earlier, possible recent changes, if any have been made, could invalidate it. This takes constant vigilance on the part of the Church and the reception of converts can be modified if the practices of other communities change. (The theory is the same for all Orthodox but the line of acceptability for some is application of water in the name of the Trinity and for others immersion (or as close as possible to it) in water in the name of the Trinity. It is the way water is applied that is at issue and not whether baptism in itself is acceptable (either outside or on reception) or whether Roman Catholics are in error, which reception of converts other than directly communing presupposes. Everyone would agree that if Roman Catholics stopped using the name of the Trinity, water or baptism although then they could not be accepted without Baptism, even if all else remains equal. The affect of the rite of Baptism (or its validity) outside the Church is another matter than how to receive converts. For this the rite used is the essential matter.
The influence of or reaction to western churches/thinking has also played a large part in the way baptism was received. It takes quite a bit to unpack all these influences and to extract legitimate practice from that which was mistaken; not to re-mention the strong evidence of the legitimacy of different practices.
Note: it seems strange to me that people accept the judgement of the neophyte Orthodox churches in the US rather than the judgement of the centuries old centre of Orthodox spirituality on Mt Athos and consider these monks as “ultra-traditionalists” misguided by a Saint named Nicodemos. Hmm…
Regarding valid and not valid, I think that only a distinction between ritual form and Spiritual transformation of a Mystery can help in this matter, such as without the Spirit transforming the gifts on the Holy Table they would remain only bread and wine even if the service is done in all other respects validly. Does the performance of the ritual of itself force the Spirit to transform it to its spiritual reality or is He free to transform only those performed legitimately within the Church? (Perhaps the whole circumstances of the ritual, in deed and thought, will be honoured by the Spirit without fail, including not only the immediate rite but also the canonical/creedal position of the Priest and the local Church within which he serves.) I think that there may be a valid form but an invalid Mystery because it is not transformed by the Spirit. The need of Chrism for converts supports this idea because it implies the absence, in Mystical/Sacramental terms, of the Holy Spirit. The question is whether the form can be transformed at a different time to its application.