Maybe a silly question, but on Great Feast days (I'm wondering about Pentecost, specifically) are the saints who would usually be commemorated that day still commemorated? I think I remember that being the case, but it's not something I've paid close enough attention to yet where I would feel confident in my memory.
There is a liturgical book called the Typikon, which tells you what to do when this happens.
This book, which I can furnish you some English editions of, can vary quite a bit between jurisdictions, and even parishes and monasteries, that exists in two main forms: the Violakis Typikon from the 19th century used mainly by the majority of Greeks and Antiochians, and the older Sabaite-Studite synthesis, which exists in two broad flavors, an ancient Studite-Sabaite version used by the Russian Orthodox Old RIte parishes like The Church of the Nativity in Erie, PA which has longer services, and a somewhat newer version that is very widely used, by all the Slavonic churches, and on Mount Athos, and in Jerusalem (and the Monastery of St. Catharine in Sinai). There is also a disused Cathedral Typikon that was used at the Hagia Sophia in Constantinople and in the cathedrals in Thessaloniki and Athens until the brutal Venetian invasion of the Byzantine Empire in 1204, which has been reconstructed by Dr. Alexander Lingas, and features services that are in some respects simpler, but in other respects more demanding in terms of requiring large numbers of deacons and psaltis in order to sing. The Violakis Typikon was ostensibly inspired by this, but really its more of a simplification of the Sabaite-Studite typikon, based on local variations and liturgical customs, and it has some features that Metropolitan Kallistos Ware famously described with great understatement as “Ill advised.”
At any rate, what the Typikon does is it tells you how to celebrate the services, for example, what to do when a fixed feast coincides with the movable feasts of the Lenten-Paschal cycle. The fixed holy days are contained in the Menaion, the most important feasts of our Lord and the Theotokos being in the Festal Menaion (of which Metropolitan Kalllistos Ware, memory eternal, did a wonderful translation with Mother Mary, memory eternal), and the Monthly Menaion, which used to be inaccessible, is now online in full thanks to st-sergius.org and another site, and it contains most of the feasts for individual saints (as most of them do not rise to the level of importance to be included in the Festal Menaion). The services of Pre-Lent, Lent and Holy Week are contained in a hymnal called the Triodion, and then on Pascha, last Saturday evening at Paschal Nocturns, you switch from the Triodion to the Pentecostarion - the best Triodion translation I’ve seen is the Metropolitan Kallistos Ware edition (also with Mother Mary), which comes in two books, one of which contains the weekday services for the Pre Lent and the second through sixth week of Lent (thus, most of the Presanctified liturgies), whereas the best Pentecostarion I’ve seen is the St. John of Kronstadt, and these versions are in my library (I do not own the complete twelve volume monthly menaion in print format, in part because of the problems I’ve been having handling books; but I do have digital access to it, both through st-sergius.org and another resource.
St-sergius.org also contains a Triodion, Pentecostarion (the Russians call it the Flowery Triodion, which is a misnomer, because the Triodion takes its name from the Triodes, distinct three-ode canons sung at Matins on the weekdays in Lent, not to be confused with the type of vacuum tube, whereas there are no Triodes in the Pentecostarion. But if you abbreviate the Canon during Bright Week so as to sing only two of the eight odes, you get a Light-Emiting Diode.
By the way, with the older typikon, and do not use the Revised Julian Calendar, but rather the Julian Calendar or the Gregorian Calendar something really special happens when Pascha and the Annunciation happen on the same day: a Kyriopascha. This last happened in 1991, and will next happen in the 2070s.
However, the Finnish Orthodox use the Gregorian Calendar, but they also use the traditional Typikon, more or less (the Finnish church is not as traditional as I would prefer), so in theory, they should be celebrating a Kyriopascha in the 2030s, I think in 2034.