it depends if there are questions in the app about previous applications. if there are, then you need to be honest and explain. there is no harm in it, and it probably won't affect your current application. if you do no provide this information and lie in the application, that leads to much worse problems. was the application approved or was it withdrawn?
again, only answer the questions that are asked and if any of this is relavant to questions in the app, then you MUST answer truthfully and provide an explanation. If the explanation is as simple as you weren't ready to move to canada during that time, then I doubt it would cause issue. If it was related to your relationship, then it could possibly trigger additional relationship proof requests or an interview - though if your current application is solid and you're still together 4-5 years later, i doubt this would happen either. Bottom line... DON'T LIE IN YOUR APPLICATION!
i really wouldn't rely on an MP's secretary on information about submitting an application, unless they specifically went through spousal sponsorship. Remember, this is your life and future, not theirs, so they won't pay the consequences of a major mistake like that, only you will. Really, the only thing the MP's office should be relied on for is getting information about why your application is stuck and not processing.
