Audit what clients actually receive
Collect one example of every document a client might see in a typical year. Include letters, proposals, monthly reports, statements, reminders, invoices generated through client software and anything sent by email automatically. Lay them out together, on screen or on a table, and look at them as a client would.
Inconsistencies usually jump out quickly: an old logo on a reminder template, different fonts on reports produced by different staff, or a colour that drifted over time. Note each difference and who controls that template. The audit becomes your to-do list for bringing everything back into line.