Why is new members' money worth more than old members' money?
Jamie wrote....
My club has added several new members lately, and after inputting their contributions, I noticed that their payments were suddenly worth more than they had paid--for example, a $520 deposit was worth $550. However, the old members' valuations, for the most part, are well below what they paid in. Why isn't every member valued at the same  percentage of their contribution if everyone is sharing the same portfolio?
Member payments (contributions) purchase units in the club based upon the current unit value when the payments are made.   Therefore, payments made at different times will perform differently.    In other words,  in your situation the old members' purchased a greater number of units in the club when the unit value was high and the new members' purchased a greater number of units in the club when the unit value was low.    
The same effect can be seen in the following example.   Let's assume you invested $1000 in MSFT stock a year ago at $75 per share.  A friend invested an equal $1000 into MSFT 6 months ago when the price was just above $40.  Today, you've both invested $1000 into MSFT and the current price is $65.   Your money has been invested longer but your investment is worth less.  Your friends equal amount of money hasn't been invested as long but the stock is now worth more than the original investment.   
In either case, your club or the MSFT example, had the value of the unit or stock gone up rather than down when the later investments were made,  the earlier investments would have been worth more than the later investments.  
Thanks for using bivio!
Jerry Dressel
St.Louis, Missouri