Well presuming this is a case in a Thai court, this is the standard on a Thai insurer application:
WARNING: Office of Insurance Commission (OIC.) The applicant should disclose all the facts you know. Any nondisclosure shall make the policy issued hereunder voidable.
The Company has the right to void the contract according the Civil Commercial Code Section 865.
So just from the above, the insurance company could say you knew about such pre-exiting conditions. You just chose not to disclose ALL of them.
But since this is a WrLife topic, their application form states:
MEDICAL PREEXISTING CONDITIONS (IF ANY):
past or present sickness, past surgery,
medicine taken:
NB: with no time reference i.e. last 5 or 10 years
Personally, I had no problem with the above from WrLife as I had just completed a life insurance application at age 70 (accepted) where I provided a medical history going back to arthroscopic knee surgery in 1998.