What must be submitted from the contractor under FAR clause 52.243-4 -- Changes to assert the right to adjustment?
"What must be submitted" is, as you stated in your question, "a written statement describing the general nature and amount of the proposal." The term "general" provides some leeway, but the phrase "...unless this period is extended by the Government" at para. (e) of 52.243-4 provides even more. Just as importantly, the clause prescription line states: "The 30-day period may be varied according to agency procedures." So, the contracting officer has some discretion as to how strictly to enforce both the content and the timing requirements of the contractor's adjustment notification. Good business sense and fairness should prevail. You should also consult with your organization's legal counsel on this type of issue.