Inviting multiple single-board Guests to a board simultaneously will trigger the multi-board Guest message when it shouldn't

Issue Summary

When inviting multiple single-board Guests to a board simultaneously (more than 100 users), these invites might be rate-limited by our API, resulting in these invites not being sent. When that happens, Trello will end up triggering the multi-board Guest message instead of informing the user they're being rate-limited. 

Steps to Reproduce

• Open the board
• Try to invite more than 100 users to the board
• Then, try inviting another list of 100 users
• You'll notice the invites didn't go through, and the multi-board Guest message was triggered.

Expected Results

Users shouldn't be warned about single-board Guests becoming multi-board Guests when multiple Guests are invited simultaneously to their boards. They should instead be informed they're being rate-limited and should try again later. 

Actual Results

Users are receiving a warning that single-board Guest(s) will become billable members when they're only being invited to one board.

Workaround

The user can wait 5 min before sending the next batch of invites. This will ensure they won't be rate-limited, and consequently, the multi-board Guest message won't get triggered.