I have been doing some further study, and it does seem that although the Byzantines are the only Orthodox community to preserve the use of a presanctified liturgy, nevertheless it would appear to be the case that this rite was formalised by St Severus himself, based on the practice of hermits in the 6th century.
It does seem to have died out in the Oriental Orthodox communion after the 13th century. But since St Severus was in exile in Egypt for 20 years, it would be interesting to see if the pre-sanctified liturgy was introduced there, and if it is possible to determine when the reservation of the sacrament ceased in Egypt.
In the Syrian practice, based on St Severus' instructions, the pre-sanctified liturgy would appear to have been based on the Vespers service. A portion of the reserved Body of our Lord would be used to 'sign' a chalice of wine. It appears that this form of prayer would be used during weekdays in Lent, as is the case in the Byzantine communion.
Certainly as others have posted in other threads, we cannot and should not develop a revisionist description of Orthodox history which excludes any possibility of change. Things were different in the past, while things were also the same. Being aware of the distinction, and the reasons behind the distinction are not something to fear but something that will help us be truly Orthodox in the 21st century.