TLDR: You could formalize the commitment through a preliminary reservation agreement referred to in Article L. 261-15 of the CCH, signed and then filed with the notary or registered with the tax office. For the extension applicable to acquisitions made between January 1 and March 31, 2013, you had to prove that a commitment had been made no later than December 31, 2012.
The preliminary reservation agreement
For a property acquired off-plan, the commitment to make an investment could take the form of a preliminary reservation agreement provided for in Article L. 261-15 of the French Construction and Housing Code.
You had to sign this agreement and then file it with the notary’s records or register it with the tax office.
The deadlines to meet
This procedure applied to preliminary reservation agreements signed and filed or registered no later than December 31, 2011. The corresponding notarized purchase deed then had to be signed no later than March 31, 2012.
The extension applicable in 2013
The extension of the Scellier scheme concerned acquisitions of new properties or properties acquired off-plan made between January 1 and March 31, 2013. The acquisition date corresponded to the date on which the notarized purchase deed was signed.
To benefit from this extension, you had to prove that you had made the commitment to carry out the real estate investment no later than December 31, 2012. If you could not prove this, the tax reduction could not apply to the acquisition of the property acquired off-plan.