title: vlookup values from other sheets disappear when file closed
body: <p>I've got a group of registers that I created for our volunteers and youth club members. Each register spreadsheet is from Sept to July. More and more volunteers and young people are staying with us for longer so I have been trying to create a vlookup that takes the total hours they volunteered from the previous years and add it to the current year total. This chains about 3-4 previous years of registers together. ie, 2014-15 adds to 2015-16 total, 2015-16 adds to 2016-17 total, 2016-17 adds to 2017-18 total, etc. The vlookup works great when all the previous years registers are open, but once I close one I get a #n/a error. How can I prevent the error msg and keep my formula working without opening all the documents?</p>