Currently a 5E (2014) user of a long-standing campaign

[SmackDaddy]

Been playing this campaign for 2 years now at least (and more to come) -- if i were to update to primary three 5.5E (2024) books, what would I expect as far as loss of data or needing to redo something?

[superteddy57]

Enabling the 2024 (5.5) modules won't cause a loss of any data. You can actually enable the ruleset automation for that version right now with no cost. The modules just provide the records to make those types of characters and using those NPCs.

[Nylanfs]

Also make sure you are following the 3-2-1 rule and backing up your campaign data regularly. :D

[SmackDaddy]

Absolutely