Explanation:

Option A is correct: The GIPS (Global Investment Performance Standards) standards require that compliance must be applied on a firm-wide basis. This is a fundamental requirement of GIPS compliance - a firm cannot claim compliance for only some of its products or portfolios while excluding others.

Option B is incorrect: GIPS does not allow for partial compliance claims. A firm cannot state it is "in compliance with the GIPS standards except for..." This would be considered misleading and non-compliant with GIPS requirements.

Option C is incorrect: A firm cannot refer to its performance calculation methodology alone as being "in compliance" with GIPS standards. GIPS compliance applies to the entire firm's performance presentation and reporting practices, not just the calculation methodology.

Key GIPS Compliance Requirements:

1. Firm-wide application: GIPS standards must be applied to all of the firm's discretionary portfolios.
2. No partial compliance: Firms must either be fully compliant or not claim compliance at all.
3. Comprehensive compliance: Compliance includes all aspects of performance calculation, presentation, and disclosure, not just methodology.
4. Verification: While verification is recommended, it is not required for claiming compliance, but firms must comply with all requirements to make a claim.