Revert Date.parse check for DisclosureDate

An approximation of https://en.wikipedia.org/wiki/Robustness_principle.

tools/dev/msftidy.rb

@@ -441,10 +441,18 @@ class Msftidy
 
     # Check disclosure date format
     if @source =~ /["']DisclosureDate["'].*\=\>[\x0d\x20]*['\"](.+?)['\"]/
-      begin
-        Date.parse($1)  #Captured date
+      d = $1  #Captured date
       # Flag if overall format is wrong
-      rescue ArgumentError
+      if d =~ /^... (?:\d{1,2},? )?\d{4}$/
+        # Flag if month format is wrong
+        m = d.split[0]
+        months = [
+          'Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun',
+          'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'
+        ]
+
+        error('Incorrect disclosure month format') if months.index(m).nil?
+      else
         error('Incorrect disclosure date format')
       end
     else