Since no official Notice to Proceed letter was provided to the contractor, does the implication of the letter submitted to the contractor provide for the Notice to Proceed if no objections were made to the letter and in light of the fact that the contractor complied with a Construction Schedule? Is there a reference in the FAR which allow for the reliance of the government on the contractor's Construction Schedule as the performance tim establishment?
You need to obtain the opinion of legal counsel to establish the legal sufficiency of the referenced letter or compliance with the Construction Schedule versus a formal Notice to Proceed, but a clue can be taken from FAR 36.213-4. It states:
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"When a notice of award is issued, it shall be done in writing or electronically, shall contain information required by 14.408, and shall --
(e) Specify the date of commencement of work, or (my emphasis) advise that a notice to proceed will be issued."
In other words, generally speaking the work does not have to be tied to a NTP for the work schedule to be legally established. However, a question arises when you consider that a clause (such as the one at FAR 52.211-10) ties the completion date specifically to the receipt of a Notice to Proceed. The contractor could theoretically tie not receiving a NTP to not being obligated to a specific completion date. Issuing a NTP is the clear responsibility of the Government. If this issue ever went to court, the burden would be on the Government. That's why it's important to consult with legal counsel for a definitive response to your question as to what constitutes "acceptance" in this specific situation.