In Aion we have the "usual" Terms and Conditions applying for multiple accounts, stating:
4.1 Unless the Rules allow exceptions, the user may participate in each round of an online game (e.g. world, universe etc.) using one user account only. It is not permissible to use multiple user accounts ("multi-accounts"). Gameforge is entitled at any time at its own discretion to block or delete unauthorised multi-accounts.
However, we do have the mentioned "Additional game rules" that were mentioned in both Discord and here on the forum:
These obviously state:
You are more than welcome to use more than one account at a time, however this must obey the rules of the ToS. This means you are not allowed to AP trade using these to accounts or use an alt account to insult a player of the opposite faction.
On Discord, multiple (former) CMs stated that these rules do only apply on retail servers. However, there is no special thread mentioning special rules about classic. There is one thread in a neutral part of the forum. Therefore, everyone has to assume it does apply to any of the servers and game versions.
I do not know either why "multi-account" is defined as "accounts being online at once". I can provide numerous examples from Gameforge games where people got banned referring to the rule in the T&Cs because they had more than one account. No matter, if it's online at the same time or not. Even the T&Cs obviously prove your definition wrong. So no, contradictory to your statement on Discord, Drestam I wouldn't call this self-explanatory. It's misleading if you state it's prohibited, though you only want to state that logging them in at once is. Still, this is nowhere mentioned in the additional game rules, which make the T&Cs invalid by default.
So according to the game rules and T&Cs it's nowhere prohibited to use one account on Classic servers (leaving aside the way you do it). However, if you claim that it's not permitted, the rules should've been worked on. Stating something on Discord with no foundation and possibly even punishing players violating some rule that doesn't exist... is quite questionable. If you need additional game rules for Classic, work on them. It's been more than a month now and even if it does not concern me personally it's an obvious flaw.