How do I prevent AppleScript from using short numbers?
An AppleScript function convertNumberToString is provided by Apple.

Mac Automation Scripting Guide: Manipulating Numbers


  Converting a Long Number to a String
  
  In AppleScript, long numeric values are displayed in scientific notation. For example, 1234000000 is displayed by a script as 1.234E+9. When this value is coerced to a string, it becomes: "1.234E+9". The handler in Listing 20-3 converts a number, regardless of length, to a string of numeric characters instead of a numeric string in scientific notation.

on convertNumberToString(theNumber)
    set theNumberString to theNumber as string
    set theOffset to offset of "E" in theNumberString
    if theOffset = 0 then return theNumberString
    set thePrefix to text 1 thru (theOffset - 1) of theNumberString
    set theConvertedNumberPrefix to ""
    if thePrefix begins with "-" then
        set theConvertedNumberPrefix to "-"
        if thePrefix = "-" then
            set thePrefix to ""
        else
            set thePrefix to text 2 thru -1 of thePrefix
        end if
    end if
    set theDecimalAdjustment to (text (theOffset + 1) thru -1 of theNumberString) as number
    set isNegativeDecimalAdjustment to theDecimalAdjustment is less than 0
    if isNegativeDecimalAdjustment then
        set thePrefix to (reverse of (characters of thePrefix)) as string
        set theDecimalAdjustment to -theDecimalAdjustment
    end if
    set theDecimalOffset to offset of "." in thePrefix
    if theDecimalOffset = 0 then
        set theFirstPart to ""
    else
        set theFirstPart to text 1 thru (theDecimalOffset - 1) of thePrefix
    end if
    set theSecondPart to text (theDecimalOffset + 1) thru -1 of thePrefix
    set theConvertedNumber to theFirstPart
    set theRepeatCount to theDecimalAdjustment
    if (length of theSecondPart) is greater than theRepeatCount then set theRepeatCount to length of theSecondPart
    repeat with a from 1 to theRepeatCount
        try
            set theConvertedNumber to theConvertedNumber &amp; character a of theSecondPart
        on error
            set theConvertedNumber to theConvertedNumber &amp; "0"
        end try
        if a = theDecimalAdjustment and a is not equal to (length of theSecondPart) then set theConvertedNumber to theConvertedNumber &amp; "."
    end repeat     if theConvertedNumber ends with "." then set theConvertedNumber to theConvertedNumber &amp; "0"
    if isNegativeDecimalAdjustment then set theConvertedNumber to (reverse of (characters of theConvertedNumber)) as string
    return theConvertedNumberPrefix &amp; theConvertedNumber
end convertNumberToString