Upvote:1
The Emperor, like other members of the reichstag or imperial diet, would be present in person or send an accredited representative to the meetings.
In 1663 the imperial diet met at Regensburg and never dissolved, the Perpetual Diet of Regensburg. Since rulers of states couldn't spend all their time at Regensburg, they sent representatives to the Perpetual Diet.
Previously, the Diet had been convened in different cities but, beginning in 1594, it met only in the town hall in Regensburg. On 20 January 1663, the Diet convened to deal with threats from the Ottoman Empire (the Turkish Question).[2] Since the Peace of Westphalia in 1648, the Holy Roman Emperor had been formally bound to accept all decisions made by the Diet. Hence, out of fear that the Emperor would disregard the Diet's role by not calling sessions,[4] it never dissolved and became a perpetual diet. Therefore, no final report of its decisions, known as a Recess, could be issued, and that of the preceding diet, issued in 1654, was dubbed the Youngest Recess [de].[5] From 1663 until the 1684 Truce of Ratisbon (a former name of Regensburg in English), the diet gradually developed into a permanent body.[2]
In addition to envoys who represented the Imperial Estates in the Diet, Regensburg had around 70 representatives (Komitialgesandtern or Comitia) from foreign states. The Emperor was represented by a Principal Commissioner (Prinzipalkommissar), a position that accrued to the Thurn und Taxis family from 1748.
https://en.wikipedia.org/wiki/Perpetual_Diet_of_Regensburg
So after about 1663, the deliberations of the College of Electors in the Diet would be carried by representatives of the Electors (including the Emperor as King of Bohemia) instead of by the Electors in person.
After about 1663 the Electors would only meet in person to elect an Emperor.
The Emperor would always have a representative at the diet when he was not there in persons, to present him as the holder of his various principalities which had votes, and as Elector of Bohemia, and as Emperor.
So possibly after 1663 all mention of the Elector of Bohemia's representative would describe him as the Emperor's representative, since the position of Emperor was the highest position in the Empire, and since everyone knew that the Emperor's representative was also the representative of the King and Elector of Bohemia, the Archduke of Austria, the Duke of Styria, Carinthia, and Carniola, etc.
That is my guess.
Possibly an expert on Holy Raman Empire history will give a more authoritative answer.