Daydate Assistance Required

[N.J.L.]

If any one could cast some light onto what I may have here.

The case number is 8XXXXXX and the model number is clearly stamped as 18158. A number I do not recognise.

Could the watch have originally been a diamond bezel and diamond dial model or possibly a standard 18k model with a diamond dial added later?

Could the case number represent a replacement case from Rolex?

The piece is in excellent woking order.

Any feed back would be appreciated.