This is a complicated issue. A few points:
1. To maintain a monogram license, you must be able to demonstrate capability to manufacture the equipment within the scope of that license and have complete design packages. The API Monogram Licensing Program Requirements includes the following regarding design packages (emphasis added):
"The API Monogram Licensing Program requires the selection of a design package for review during initial, surveillance and renewal audits."
"Design Package (therefore is) – a detailed plan for a product which includes all the background documents, applicable API standards, and the instructions, procedures, specifications, drawings, routings, travelers, checklists, process sheets and changes to these documents necessary to produce that product at the manufacturing location. Such documentation shall include, but not be limited to, design plans, input elements, output elements, evidence of review/verification and evidence of validation. Since the purpose of the API Monogram Program is to consistently, objectively, and reliably identify organizations who are capable of manufacturing products that comply with the current edition of the applicable API specifications, the organization shall have a complete design package, as well as procedures that provide instructions and requirements on how to develop a design, unless eligible for design exclusion."
Note 4F, 7K, and 8C are not eligible for design exclusion because they are not listed in API Advisory 6.
Based on the above, in order to have a monogram license, you are required to have a design package that includes evidence of validation for equipment within the scope of that license.
2. The API Monogram Licensing Program Requirements do not define design validation. However, API Q1 3.1.9 defines design validation as:
"Process of proving a design by testing to demonstrate conformity of the product to design requirements.
NOTE Design validation can include one or more of the following (this is not an all-inclusive list):
a) prototype tests,
b) functional and/or operational tests of production products,
c) tests specified by industry standards and/or regulatory requirements,
d) field performance tests and reviews."
Note that testing is included in the definition, but based on the example, a "field performance review" might be acceptable. Product standards sometimes require "design verification" tests, which fall within the Q1/monogram validation definition.
3. API 4F appears to have a requirement for design validation. 7K and 8C appear to have requirements for "Design Verification" tests, which would likely fulfill the Q1/monogram requirements for design validation.
You could try to perform a field performance review of equipment that you have previously manufactured and document this as design validation, but I think it is unlikely that API will accept this because it wouldn't demonstrate that you can perform the design validation/verification testing required by the standard. You likely need to perform validation/verification testing per the appropriate standard to maintain a monogram for that standard.
If you are ok with dropping the monogram licenses and maintaining a Q1 registration, then you won't have to perform validation testing per the API standards, but design validation (likely including testing based on whatever you and/or your customers want) will still be required.