I propose that we fix this issue by specifying the serial number prograssion via a date after 1900/3/1. I see two ways this could be done.
1) Replace the <table:null-date> with <table:serial-date-intercept>, the latter to be defined as:
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8.4.1.1 <table:serial-date-intercept>
The <table:serial-date-intercept> element specifies the serial number of
1904/1/1, i.e. the numeric value obtained when the date 1904/1/1 is
converted into a numerical value. This numerical value is specified in
the element's table:date-value attribute.
Note: Commonly used values are 1462, 1461, 1460, 1 and 0.
Serial numbers for dates after 1904/1/1 must equal to the serial number
for 1904/1/1 plus the number of days properly between 1904/1/1 and the
given date plus 1.
element-table:
The <table:serial-date-intercept> element is usable with the following
element: <table:calculation-settings> 8.4.1.
The <table:serial-date-intercept>> element has the following attributes:
table:date-value 17.617 and table:value-type 17.750.
The <table:serial-date-intercept> element has no child elements.
17.617 table:date-value
The table:date-value attribute specifies the serial date intercept. The
serial date intercept is the numerical value that results if the date
value 1904/1/1 is converted into a numerical value.
The default value for this attribute is 1462.
attribute-table:date-value
The table:date-value attribute is usable with the following element:
<table:serial-date-intercept> 8.4.1.1.
The table:date-value attribute has the data type number.
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2) Alternatively we could stick with <table:null-date> but would then need a more complicated description:
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The <table:null-date> element specifies the null date for a spreadsheet document. If n is the numeric value that is obtained when the date 1904/1/1 is converted to a numerical value. Then the null date is exactly n days before 1904/1/1. The null date is specified in the element's table:date-value attribute.
Numerical values for dates after 1904/1/1 must equal to the value n for 1904/1/1 plus the number of days properly between 1904/1/1 and the given date plus 1.
Note: The numerical value obtained when the null date is converted to a numerical value is typically -1 or 0.
Note: Common values for the null date are 12/31/1899, 01/01/1900, and 01/01/1904.
element-table:null-date
The <table:null-date> element is usable with the following element: <table:calculation-
settings> 8.4.1.
The <table:null-date> element has the following attributes: table:date-value 17.617 and
table:value-type 17.750.
The <table:null-date> element has no child elements.
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Solution 1 has the benefit of being simpler, solution 2 the benefit of retaining the null date.
Bug
Minor