Tourist Visa - Previous visa refusal reference # required?

Hi,

This is my first time posting here so if I'm posting on the wrong sub-forum, please redirect me to the correct one.

So I recently applied for a short-stay tourist visa for the UK (from the US). As a background, I was refused a UK visa last year (for Family Visitor). Afterwards, I reapplied with the correct application (Student visitor) and was issued a visa.

This year, I noticed when I was filling out the online application, I did not see any instruction that asked for a reference number for refusal visa for UK. So I thought it is not required (I could at least added this to the additional info all the way to the end but it slipped my mind).

What are the chances of being refused (for my current visa application) for not providing the reference number for previous visa refusal? I'm a bit paranoid due to being rejected last year.

Any thoughts from anyone with experience would be much appreciated! I could still forward the information to the UK visa centre but not sure if this reference number is necessary, since they haven't asked for any additional documents/info so far...