The phrase "unreliable data" means that the information or facts being used or referred to cannot be trusted or relied upon to be accurate or true. Full definition
The implementation took two years longer than expected because of unreliable data in the system. (canadianbusiness.com)
At present some people seem to think that the number of stations with unreliable data is small and could not possibly impact the large data sets on which climate science is based. (realclimate.org)
All real estate is local but the more local you go, the fewer the sales and the more unreliable the data becomes. (myseattlehomesearch.com)