any sum or sums heretofore certified in favor of the carrier under § 209 of the Transportation Act, 1920, is necessary to make good to said carrier the guaranty provided by the said section. The Commission hereby certifies that such amount of six million dollars ($6,000,000) cannot be reduced by further accounting or otherwise,” with which was coupled a statement that additional amounts might be found to be owing on further investigation.
The respondent, armed with this certificate, procured from the Treasury the $6,000,000 required for its present needs. This amount added to the earlier payments of $6,500,000, makes up a total of $12,500,000 collected on account of its claim against the govérnment. The total was nearly $6,000,000 less than the amount claimed by the respondent to be ultimately due. It was about $3,200,000 less than the estimate of the final payment submitted as a basis for the certificate in a report to the Commission by the Bureau of Finance. Whatever the final payment might afterwards be found to be, the sum certified to be due left or seemed to leave a margin of error ample enough for any change within the zone of reasonable expectation.
The Commission, after satisfying thus the instant needs of the respondent, continued the investigations necessary to ascertain the final balance. Not till five years had passed was it ready to announce its findings. In the meantime it had filed a series of reports or decisions defining or revising the principles and formulae that were to govern it thereafter in the allowance or disallowance of expenditures for maintenance. See, e. g., Maintenance Expenses under § 209, 70 I. C. C. 115; In the matter of Final Settlement under § 209 of the Transportation Act, 1920, 70 I. C. C. 711. By its final certificate issued on June 8, 1926, under § 209 (g), it certified that the total amount necessary to make good the guaranty was