This is from the Yamaha website indicating if you can provide proof you have done the service with receipts, you should be covered
YAMAHA OUTBOARD WARRANTY POLICY
b) The CUSTOMER has followed the break-in and storage instructions contained in the Owner's Manual, and all other instructions shown in the Owner's Manual;
c) The CUSTOMER can provide record of maintenance having been performed as recommended in the Owner's Manual;
d) Requests for repairs under warranty have been made as prescribed in Section D.
2. This warranty does not cover the repair of damage resulting from abuse or neglect of the OUTBOARD. Examples of abuse and neglect include, but are not limited to:
a) Racing, competition use, modification of original parts, abnormal strain;
b) Use of lubricants, oils and fuel/oil mixtures other than those recommended in the Owner's Manual, improperly installed accessories or use of parts or accessories that are not equivalent in design and quality to genuine Yamaha parts.