How to allow meeting requests that occur in the past

We have an equipment resource calendar that we use to keep track of usage.  It has delegates that accept the meeting request. The problem is the users would like to allow meeting requests that occur in the past because sometimes they don't put things in in advance, but they want to document the use.  Every time a meeting request is sent with the date in the past:

Your meeting request was declined.
The invitation was declined because it occurred in the past.
________________________________
Sent by Microsoft Exchange Server 2013

Here is the configuration as it stands now:

RunspaceId                          : cd6e516b-a2c2-4933-8c4d-286f23fef449
AutomateProcessing                  : AutoAccept
AllowConflicts                      : True
BookingWindowInDays                 : 365
MaximumDurationInMinutes            : 0
AllowRecurringMeetings              : True
EnforceSchedulingHorizon            : True
ScheduleOnlyDuringWorkHours         : False
ConflictPercentageAllowed           : 0
MaximumConflictInstances            : 0
ForwardRequestsToDelegates          : True
DeleteAttachments                   : True
DeleteComments                      : True
RemovePrivateProperty               : True
DeleteSubject                       : False
AddOrganizerToSubject               : False
DeleteNonCalendarItems              : True
TentativePendingApproval            : True
EnableResponseDetails               : True
OrganizerInfo                       : True
ResourceDelegates                   : {xxxxx/Users/Field Operations/xxxxxxx, xxxxx/
                                      Users/Headquarters/xxxxxxxx, xxxxx/Users/Headquarters/xxxxxx}
RequestOutOfPolicy                  : {}
AllRequestOutOfPolicy               : False
BookInPolicy                        : {}
AllBookInPolicy                     : False
RequestInPolicy                     : {}
AllRequestInPolicy                  : True
AddAdditionalResponse               : False
AdditionalResponse                  :
RemoveOldMeetingMessages            : True
AddNewRequestsTentatively           : True
ProcessExternalMeetingMessages      : False
RemoveForwardedMeetingNotifications : False
MailboxOwnerId                      : xxxxx/Exchange/Resources/NameOfResourceList
Identity                            : xxxxx/Exchange/Resources/NameOfResourceList
IsValid                             : True
ObjectState                         : Changed

Sally