The local class associations and the GC are still working on this, so the details below are subject to change.
A boat will be class legal and entitled to a Measurement Certificate if it has been measured in by a recognised F16 Class Measurer (currently only Piet Saarberg or myself (I am UK measurer)), or if measured by an ISAF recognised measurer. In the latter case the boat will get an SCHRS rating but in all likelihood the measurer will complete the F16 Measurement Form as part of the measurement process and his/her official stamp on the form is acceptable for that boat to have a valid F16 certificate. In the case of 'Official' markings on a boat as set out in the rules (this is something we need to sort out at the WGM) they can be applied retrospectively by anauthorised F16 class official from the local NA on production of a completed Measrement Form.
This is how I would anticipate it working, but I add the proviso that as an infant class, we won't always be able to accommodate every individual situation.
Please also remember there are costs in getting a boat measured and a certificate issued.