City data in correct

[Irfan Saeed]

Hello Community member - I would appreciate if someone can help me on this.

I am planning to offer on a house but the house seems to have a later addition. The city data shows 1600 sqft was added and one bedroom was included. The house was originally 1550 sqft having only 3 bedrooms and 2 baths. The house according to mls data and as per viewing has 5 bed rooms and 4.5 bath rooms and 3300 sqft. my question is , if it is okay to compare this house with the houses which were originally built for the same sqft or should i discount the price in my offering. 

or is a possibility that city data can be updated with the current sqft of the house. ?

how does the arv get impacted with this kind of later addition. ?

should i have any other concern ?

Thanks