ITB is the name owners and brokers use for Spain's compulsory boat inspections. Real Decreto 1434/1999 sets them: a periodic inspection at most every five years for private boats from 6 m and for every charter boat, and an intermediate one out of the water for some boats between the second and third year. They're carried out by accredited inspection bodies, and each one is recorded on the certificado de navegabilidad.
What a surveyor checks
Read the certificate: the type and date of the last inspection, the body that did it and the next one due. A missed inspection lapses the certificate. Annex II of the decree lists the items inspected, from keel bolts to extinguishers, and is a useful cross-check for your own survey.
In the report
"Certificado de navegabilidad: last periodic inspection by an accredited body two years ago; intermediate inspection out of the water due before next season. Book it with the haul-out."