If someone provides a model number for a Hydrel fixture that does not match any fixtures we have available, it may be the part number for the ballast or lamp module, as the model number for the entire fixture is not listed in the fixture.
Many older fixtures have outdated nomenclature. Attached below are two documents that may be helpful - one document can be used to cross-reference the old module nomenclature to the new module nomenclature (be aware that the customer may not advise correctly on things like spacing, slashes, hyphens, etc).
The left column is the old nomenclature. To the right of that, you will see the updated nomenclature for that component. There will be a column that says either A (which indicates that the nomenclature is "active"), or O (which indicates that that nomenclature is "obsolete").
The other document advises which modules belong to which fixture series. This can be helpful for determining what accessories a customer may need, such as a replacement lens or door assembly.