Zend certified PHP/Magento developer

Searching for Products via searchCriteria endpoints (rest/V1/products?searchCriteria) is obscured, but via SKU (rest/V1/products/SKU) is not obscured?

When I try to ping for all products via a simple searchCriteria (rest/V1/products?searchCriteria[pageSize]=1), the total_count is a fraction of the full number of items in our catalog. Or when I search product by ID, I get an empty response for some items that I know to exist. For instance ID 42420:

PING /rest/V1/products?&searchCriteria[filter_groups][0][filters][0][field]=entity_id&searchCriteria[filter_groups][0][filters][0][value]=42420&searchCriteria[filter_groups][0][filters][0][condition_type]=eq
RESPONSE:
{"items":[],"search_criteria":{"filter_groups":[{"filters":[{"field":"entity_id","value":"42420","condition_type":"eq"}]}]},"total_count":0}

But if I try to search by the exact same product’s SKU, or any other product that is obscured via searchCriteria, I’m always successfully getting 1 result in response:

PING /rest/V1/products/WHATEVER_SKU
RESPONSE:
{"id":42420,"sku":"WHATEVER_SKU","name":"WHATEVER_SKU","attribute_s....,"search_criteria":{"filter_groups":[{"filters":[{"field":"entity_id","value":"42420","condition_type":"eq"}]}]},"total_count":1}

Our Magento administrator is telling me that if we change a setting (Stores -> Configuration -> Catalog -> Inventory -> Display Out of Stock Products to “Yes.”) then the searchCriteria’s response from Magento would be a full total_count and I would be able to search by ID. HOWEVER this setting will severely interfere with our stores.

Our Magento administrator is also telling me that he can build a new endpoint out for us via a php module. But I’m afraid to do that because we are considering an iPAAS solution that requires standard Magento REST endpoints, such as the very ones I am accessing.

Can anyone help me understand this more clearly to see if we truly need a custom module/endpoint, or is there something we are all missing here with searching by ID vs SKU? Thank you–