Properties present in metadata but failing while retrieving record using such fields

Hi,

I am working on MS Dynamics CRM integration and getting ref from WEB APIs v8.2/9.0.
To fulfill my integration scenarios I am using below REST APIs:

1. To retrieve all supported object - GET /EntityDefinitions
2. To retrieve Contact object metadata - GET /EntityDefinitions(LogicalName='contact')/Attributes

While working on Retrieve operation for Contact object GET /contacts , I come to know it supports below reference fields which targets to other objects in CRM System:

1. slaid  (Target object - sla)
2. slainvokedid  (Target object - sla)
3. parentcustomerid (Target object - account, contact)
4. preferredsystemuserid (Target object - systemuser) 
5. preferredequipmentid (Target object - equipment)

As per CRM API documentation, we can use odata $expand for the above properties. But somehow for the first 3 field mentioned above it is not working as expected. for fields 4 and 5 it is working as expected.
The first 3 fields are present in Contact metadata but if we use $expand=slaid API throws below error :

GET xxx.crm8.dynamics.com/.../contacts?$expand=slaid

Could not find a property named 'slaid' on type 'Microsoft.Dynamics.CRM.contact'

Now, I tried to debug all the above mentioned things and come to know that there is fields discrepancies in /EntityDefinitions. I could come to know and verified successfully that for fields 1-3,field name mentioned in /EntityDefinitions is wrong and actual names are mentioned below:

I am facing above field level issue in almost all supported objects of MS Dynamics CRM.
Could you please guide me here, is there any issues in EntityDefinitions APIs or am I missing something here?