Missing old passport... problem for spouse visa application?

Hi everyone.  I have a question about my future spouse visa application.

I know we are supposed to send both current and old passports.  I got a new passport a few years ago, and have since lost the old, cancelled one.  Is this going to be a problem when I apply? 

The form says to give full travel history for the last ten years.  I'm sure I can do that easily from memory.  The form also says to include old passport, or provide details of where it is.  It's... just lost.  I lost it during a move, and am pretty sure it got thrown away accidentally. 

Do you think this will be a problem?  The only things that are stamped in my new passport will be my trip back home to the US from Japan (where I currently live,)  and a possible upcoming trip to Malaysia. 

When I apply for the visa (spring of 2016, most likely,) my only trip to the UK in the previous ten years would be a trip I took to visit my fiance back in 2007.  Also a few trips to Spain and Germany for vacations, and of course my entries/exits to and from Japan and the US. 

If I tell them that the old passport is lost, and provide dates of my trips 2006-2016, will that be enough?  I mean, there really isn't any way to get an old passport re-issued... 

I assume they ask for the travel history to see whether the couple visited each other, but my fiance has been here with me in Japan for five years now, so we have plenty of other evidence of living together long-term.

What do you think?  I'm stressing myself out over it... should I worry?

Just be honest. It's lost. Tell them it's lost. It's not a big deal.

I just worry that they will want info that I can't remember, like travel history from further back than the ten years the app asks for... 

I just worry that they will want info that I can't remember, like travel history from further back than the ten years the app asks for... 

Just give as many details as you can remember - even if it's just an estimated month and year.

Do you still have e-tickets or itineraries from your trips over the last 10 years that could help you remember them?

I have a misplaced passport as well (I think it's in a box in my parents attic).  My way of figuring out past travel and dates is looking at the photos on my computer. 

I have a misplaced passport as well (I think it's in a box in my parents attic).  My way of figuring out past travel and dates is looking at the photos on my computer. 

Did they accept just the dates, or did they want "official" verification of some sort?

Just give as many details as you can remember - even if it's just an estimated month and year.

Do you still have e-tickets or itineraries from your trips over the last 10 years that could help you remember them?

I think I can remember the last ten years. It's them asking for dates further back that I'm worried about. Not sure I have any information left from that long ago...