ZAU CTLR EXPERIENCED OPERROR AT FL300 WHEN READBACK FROM PLT WAS ABSENT AND OR INCORRECT.

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E145 WAS ISSUED CLRNC 'AMEND ALT; CLB AND MAINTAIN FL290.' PLT CLIPPED INITIAL WORD BUT REPLIED '...(CLIPPED) TO FL290?' WITH A QUESTIONING TONE AS TO THE ALT. I RE-STATED 'AFFIRMATIVE FL290.' PLT REPLIED '290.' PLT CONTINUED TO CLB THROUGH FL290 TO FL330 WHICH WAS THE ORIGINAL CLRNC LEVEL. UPON HEARING PLAYBACK OF TAPE; IT APPEARS PLT MAY HAVE SAID 'EXPEDITE TO FL290.' MY CLRNC WAS TEXTBOOK WITHOUT QUESTION 'AMEND ALT.' I QUESTIONED THE PLT TO VERIFY HE WAS LEVEL AT FL290 EVEN THOUGH MODE C INDICATED FL293. HE SAID NEGATIVE; HIS CLRNC WAS TO EXPEDITE TO FL290. EXPEDITE WAS NOT PART OF ANY CLRNC OF HIS OR ANY OTHER ACFT ON THE FREQ AT THAT TIME. HIS READBACK INDICATED HE WAS CLBING TO FL290; NOT THROUGH FL290. THERE WAS A SUBSEQUENT PHONE CALL BTWN THE PLT AND OUR OMIC. THE PLT STATED HE SAW THE TFC AT FL300 AND LEVELED OFF AT FL290; THEN RESUMED CLB AFTER PASSING TFC. TFC IN THE SECTOR WAS COMPLEX. THERE WERE FLOW CTL INITIATIVES ADDING TO COMPLEXITY AND AUTOMATION PROBS AT THE TIME OF THE ERROR. ERROR WAS DISCOVERED THROUGH CONFLICT ALERT OEDP. I BELIEVE MY CLRNC WAS CLR AND LEFT NO ROOM FOR QUESTION OR DOUBT. ZAU IN YRS PAST HAD A LCL SUPPLEMENT TO THE 7110.65 REQUIRING CTLRS TO RECEIVE A 'COMPLETE READBACK.' THIS SUPPLEMENT WAS ALLOWED TO EXPIRE AND WAS REMOVED A LONG TIME AGO. MAYBE IT WOULD BE BENEFICIAL TO REINSTATE THIS POLICY.