Backup history not showing - Sql server 2012

We had an strange issue that our sql server 2012 Sharepoint Databases backup daily taken by 3rd party tool
and from last few days we couldn't see the entry into MSDB database when we query the tables but when i checked the event log, it shows for all the database backup history.Could you please guide me that how can i know that why i can't see the backup history?It's started just few days back as no backup messages for those databases?Even when i query the backup history tables,
i can see only few days back backup.

Sounds to me like someone did a purge of backup history. No good backup routine goes without it although it should leave at least a month (IMHO). Please see the following for what someone may have executed or may have added to some code somewhere.

Thanks Jeff.
I am also believing that history get deleted but how can i check that?
Link shows code to delete the backup history but i need to find it out how it got deleted or what happened?
Backup running fine using 3rd part tool for many days but suddenly i got the message as databases has not been backed up for since last 6 days ans when i ran the backup history query and i found that it was showing similar without backup for those days and i checked sql log, i didn't see any error in sql log but when checked event log they i see the backup entry is there for those missing days but couldn't find the info what happened.

Are you saying that there was backup history available from before 6 days ago and that only the last 6 days was missing?

It was available, let's say Backup taking every night then it shows like
No history
No History
No History

That's not because someone was purging history, at least not using the tool I posted. The history purge will only clear from a given data back to the beginning of history, It can't leave old history and delete new.

Without more information, I'd have to say backups haven't been happening since the 7th. You should probably take a look at wherever the backup files end up being stored at to make sure you have backups and test a couple to make sure that they're viable.