In the simple, YAGNI implementation of this, when you create a new HubSpot account, most likely that will insert a new row into the accounts table, and the auto generated ID of that row will be your account ID. Therefore you need uniqueness to be enforced at that level.
If you want to start running a separate copy of the system, you need to refactor the system to move that sequence out of the database so that two different customers running on different clusters don't end up with the same account ID. This is just an example, but there are many problems like this that are caused by the assumption that the production system is a single unique system.
Everything has a solution, but want to bet that at least 20 different internal systems at HubSpot assume that the account ID in that URL is globally unique?
For example, HubSpot runs a multitenant system. URLs look like:
https://app.hubspot.com/section/$ACCOUNT_ID/etc/etc
In the simple, YAGNI implementation of this, when you create a new HubSpot account, most likely that will insert a new row into the accounts table, and the auto generated ID of that row will be your account ID. Therefore you need uniqueness to be enforced at that level.
If you want to start running a separate copy of the system, you need to refactor the system to move that sequence out of the database so that two different customers running on different clusters don't end up with the same account ID. This is just an example, but there are many problems like this that are caused by the assumption that the production system is a single unique system.