Tamil Nadu State Transport Corporation [TNSTC] — Clarification on Route Board in SETC Bus - 26/12/2021 and its impact if any

Vide PNR No. T33884795 dtd 26/12/2021 my niece and her friend were travelling from Tuticorin to Chennai in SETC - TNSTC bus.
Bus, with Regn. No. TN01AN0977, on arrival for boarding at Tuticorin had the Route Board as 170/A instead of 170 UD given in the e-Ticket. On checking up with the SETC staff it was advised to board in this bus. Journey was performed by the passengers in this bus.
Please clarify the following:
Whether it was a mistake in the Route Board or Wrong Bus was allotted against the 170 UD bus, if so Refund if any may be given.