The ecclesiastical and canonical status of the various Old Calendarist jurisdictions is complex. Some regard themselves as being the only true Orthodox Christians and thus view the mainstream Orthodox Church as being in apostasy. As such, they do not share either communion or concelebration with the mainstream churches. Other Old Calendarists (typically those "in resistance") have suspended concelebrations with mainstream clergy, but will still commune the faithful of mainstream jurisdictions. They thus see themselves as a reform movement within the Orthodox Church. The question of canonicity follows much the same sort of patterns.
Views from the mainstream Orthodox on the Old Calendarists range from trying to heal the various breaks in communion or concelebration to outright declarations that such groups are themselves apostates, that is, no longer Orthodox.