Answer:

Yes, absolutely! But, under those circumstances, the first Flat must be "compacted" to just wave-A (or B or C or D, etc.) of a larger pattern. The Zigzag that follows must then be compacted to just wave-B (or C or D or E, etc.) of the same, larger pattern.

To signal an x-wave is forming after a Flat you the following must occur. The Flat should be retraced less than 61.8% by the presumed "X-wave" AND the presumed "X-wave" should take at least 1/3 of the time of the Flat but no more than 99% of the time of the Flat.

The other way an X-wave can follow a Flat is when it is part of a Double-Three Running correction (see Mastering Elliott Wave, bottom of page 8-12). That is when wave-X is larger than the Flat (around 161.8%) and takes between 1/3 and 99% of the time of the Flat.